Here's why I'm asking that question. If you have a CHM file that is linked to an application, and you are opening that CHM FROM the application, the actual pathing that the CHM would know about might be different. So it's entirely possible that if you opened the CHM in that manner, the button would fail. Even though both CHM files are inside the same folder.

Now if you were to just find the CHM using Windows Explorer and double-click it, the button may well perform exactly as desired.

And we need also to keep in mind that in today's world, there are now two different versions of the HTML Help Viewer (used to display CHM files), With the proliferation of 64 bit operating systems, we now have a 32 bit version of the HTML Help Viewer as well as a 64 bit version of the HTML Help Viewer. So it's possible that in addition to the oddity I mentioned earlier, perhaps your application is opening the 32 bit version of the viewer and there is some issue with using the control to open the 64 bit version. I'm not saying this is what's happening here, only that it may be a factor.

I clicked on the button which displayed the message "Cannot open the file".

From your explanation, it looks like this should work.

Later, the final goal is that both the chm files will reside in the same folder after the installation of the application. Somewhere in the program files. The user has to open the main chm file from the application help button and from there, we would like to provide a link to another chm which should open in a separate window.

Okay, here's the deal. I know how to make it happen, but it will require jumping through some hoops to get there. I tried to find a nice and easy way to accomplish it, but at the moment this is the best I've come up with. Hopefully others will see this and improve upon it.

Ahhh yes. This is an odd phenomenon with CHM files. I'm not sure of the exact cause, but what happens is that when a CHM file has been opened from an application, the path that it understands is different than the actual path. Weird, eh?

You will likely need to resort to some JavaScript that deduces the path. Hang on while I go fetch that article...

Nevermind, I found the solution. Don't add in the href. I was adding it in because our style sheet wasn't styling the a link without it. I modified a styles sheet and then removed the href from the above .html code of href="#MIIM'", and now it works in subfolders.